Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

A particle travels with speed $50 m/s$ from the point $(3,-7)$ in the direction $7i-24j$ . Find its positional vector after 3 seconds.

My approach: It has travelled a distance of 150m in the direction given by the unit vector $\frac{7\hat i - 24 \hat j}{25} $ .

So, its position is now $210\hat i -720 \hat j$. But it started from $(3, - 7)$, so I have to subtract that to get $197\hat i - 713\hat j$. But I think this answer is awkward, and I may have gone wrong. So, please tell me if I am right, and if yes, can you suggest any shorter way of doing it?

share|cite|improve this question

closed as too localized by Emilio Pisanty, Qmechanic Jun 4 '13 at 13:13

This question is unlikely to help any future visitors; it is only relevant to a small geographic area, a specific moment in time, or an extraordinarily narrow situation that is not generally applicable to the worldwide audience of the internet. For help making this question more broadly applicable, visit the help center.If this question can be reworded to fit the rules in the help center, please edit the question.

up vote 3 down vote accepted

Displacement :$$\vec r_f-\vec r_i = \vec d =|d| \hat d $$

$\vec r_i$= position vector initial. ie. $3\hat i -7 \hat j$ ; $|d|=150m$ as found , and $\hat d$ is the direction .

share|cite|improve this answer
$ \hat d$ is just the unit vector I mentioned, right? – Saurabh Raje Jun 4 '13 at 12:00
@SaurabhRaje: yes that's it. – ABC Jun 4 '13 at 12:01
ie$\frac{7 \hat i - 24 \hat j}{25}$ – Saurabh Raje Jun 4 '13 at 12:01
@SaurabhRaje: There is no need to post new comments every thing you mention for.If this persist that can lead to suspension , I have seen 1 case. – ABC Jun 4 '13 at 12:04
@SaurabhRaje: It's not like that . But as you sometimes do , write a new comment for every equation it's wrong. Like ""ie.eq"" must have been a part of 1st comment itself. Don't take tension though :P. – ABC Jun 4 '13 at 12:12

Not the answer you're looking for? Browse other questions tagged or ask your own question.